Compounds represented by formula (IV) below are known to be very effective against a variety of viruses, and particularly the influenza virus.
(wherein R3 represents a hydrogen atom or a halogen atom, R4 represents a hydroxyl group that may be protected, and R5 represents a hydrogen atom, an acyl group or a carbamoylalkyl group.)
Of these compounds, the 6-fluoro-substituted pyrazinecarboxamide derivative represented by formula (V) (wherein the formula in parentheses represents the tautomer) exhibits powerful anti-influenza activity, and is an excellent antiviral agent (see Patent Document 1).

A number of methods for producing this compound are disclosed in Patent Document 1. Of these, the production method represented by the reaction sequence shown below exhibits a comparatively superior yield.
